Geologic formations may be used for many purposes such as hydrocarbon production, geothermal production, or carbon dioxide sequestration. Typically, boreholes are drilled into the formations to provide access to them. Various downhole tools may be conveyed in the boreholes in order to characterize the formations. Characterization of the formations and the fluids within them provides valuable information related to the intended use of the formations so that drilling and production resources can be used efficiently.
One type of downhole tool is a neutron tool that may be used to measure a property such as porosity of an earth formation. The neutron tool bombards the formation with neutrons either continuously from a chemical source or as a pulse from an electronic source. The neutrons interact with the formation to produce radiation that is detected by a gamma-ray detector. The output of the gamma-ray detector is then correlated to the formation property. Unfortunately, similar radiation may be present due to factors other than neutron bombardment of formations and this radiation may cause a decrease in accuracy of the measurements. Hence, it would be well appreciated in the drilling industry if measurement techniques were developed that would improve the measurement accuracy of neutron tools.